The heat capacity of two natural chlorite group minerals derived from differential scanning calorimetry

The heat capacity of natural chamosite (X-Fe = 0.889) and clinochlore (X-Fe = 0.116) were measured by differential scanning calorimetry (DSC). The sam ples were characterised by X-ray diffraction, microprobe analysis and Mossb auer spectroscopy. DSC measurements between 143 and 623 K were made followi ng the procedure of Bosenick et al. (1996). The fitted data for natural cha mosite (CA) in J mol-l K-L give: C-p.CA = 1224.3-10.685 x 10(3) x T-0.5 - 6 .4389 x 10(6) x T-2 + 8.0279 x 10(8) x T-3 and for the natural clinochlore (CE): C-p.CE 1200.5-10.908 X 10(3) x T-0.5 -5.6941 x 10(6) x T-2 + 7.1166 x 10(8) x T-3. The corrected C-p-polynomial for pure end-member chamosite (F e5Al)[Si3AlO10](OH)(8) is C-p.CAcor = 1248.3-11.116 X 10(3) x T-0.5 - 5.162 3 x 10(6) x T-2 + 7.1867 x 10(8) x T-3 and the corrected C-p-polynomial for pure end-member clinochlore (Mg5Al)[Si3AlO10](OH)(8) is C-p.CEcor = 1191.3 -10.665 x 10(3) x T-0.5 -6.5136 X 10(6) X T-2 + 7.7206 x 10(8) x T-3. The c orrected C-p-polynomial for clinochlore is in excellent agreement with that in the internally consistent data sets of Berman (1988) and Holland and Po well (1998). The derived C-p-polynomial for chamosite (Cp.CAcor) leads to a 4.4% higher heat capacity, at 300 K, compared to that estimated by Holland and Powell (1998) based on a summation method. The corrected C-p-polynomia l (C-p.CAcor) is, however, in excellent agreement with the computed C-p-pol ynomial given by Saccocia and Seyfried (1993), thus supporting the reliabil ity of Berman and Brown's (1985) estimation method of heat capacities.